Add ember-simple-auth, setup login

- Allow dropdown-buttons to render a partial

ember/app/initializers/authentication.js

@@ -0,0 +1,9 @@
+import FlarumAuthorizer from '../authorizers/flarum';
+
+export default {
+  name:       'authentication',
+  before:     'simple-auth',
+  initialize: function(container) {
+    container.register('authorizer:flarum', FlarumAuthorizer);
+  }
+};